Antidepressant Mirtazapine Studied for Fibromyalgia

Editor's comment: Mirtazapine (brand name Remeron) is a tetracyclic antidepressant. It is not known exactly how mirtazapine works but it is thought to increase the activity of certain chemicals in the brain (eg, norepinephrine, serotonin).

Significant within-group PVAS reductions from baseline were observed in all 3 groups, with the greatest improvement in the mirtazapine 30-mg group (p < 0.005); between-group difference was not significant.

The proportion of pain responders did not meet significance criteria (66.67% for mirtazapine 30 mg, 50% for mirtazapine 15 mg, 41.67% for placebo).

On the PGIC, 72.73% felt better with both mirtazapine dosages compared with 50% for placebo.

Within-group FIQ responses indicated improvement in only mirtazapine-treated groups, whereas within-group improvement for HAM-D and Patient Global Assessment was observed in all groups.

Based on our findings, the sample size requirement (80% power, 5% type I error) should be 83 per group to detect PVAS change difference between mirtazapine 30 mg and placebo.

Common mirtazapine-related adverse events were increased appetite and weight gain.

CONCLUSIONS: Patients with FMS taking mirtazapine exhibited within-group significant improvement in most of the measured outcomes. Between-group analysis was predictably compromised by the small sample size. Mirtazapine was well tolerated. Further study with a larger sample size is likely to be useful.